This invention relates to a wireless communication system having one or more wireless transmitters transmitting data to one or more wireless receivers and, more particularly, to a wireless communication system in which a relatively low cost wireless transmitter transmits data to one or more wireless receivers without any communication from the wireless receiver.
Wireless transmitters have been used to transmit a condition such as temperature, humidity, temperature/humidity, or pressure, for example, from a predetermined location to a wireless receiver remote from the transmitter. These predetermined locations do not necessarily have any available power source other than a battery because they may be inside of a refrigerated space, a trailer, or an unmanned remote weather station, for example. The receivers usually have an electrical power source so that they do not have the problem of a battery as their only available power source.
Accordingly, various types of wireless communication systems have been suggested to provide power to the transmitter other than a battery. However, these have required a transceiver instead of only a transmitter at the remote location to receive a signal or sensing of the occurrence of an external event, for example, to cause transmission of data. That is, the power has been turned off in the previous transceivers until an external signal is received, but the previous transceivers have required a relatively significant amount of power to operate. This relatively significant amount of power results in a battery having a relatively short life for a relatively low cost battery or having to be a relatively expensive battery. Additionally, a transceiver increases the cost relative to a transmitter as does the event sensing hardware.
Furthermore, the transmission of signals from more than one wireless transmitter to a wireless receiver must be controlled to prevent collisions of the data packets from the different transmitters. If a collision occurs between two data packets from two different transmitters, the data is lost from both of the transmitters.
Various methods of avoiding collisions of the data packets from different transmitters have been suggested. These include using a different frequency for each transmitter or controlling activation of each of the transmitters from the receiver so that they are activated at different times. Each increases the cost.
There also have been suggestions of randomizing the time when the data is transmitted from each of the transmitters to avoid collisions of the data packets. However, randomization usually has been limited to the receiver controlling when the transmitter is activated.
Therefore, randomization has previously required a transceiver rather than only a transmitter. As previously mentioned, a transceiver increases the cost and also requires the utilization of additional power because of the transceiver being activated a relatively longer period of time than a transmitter and because of the additional hardware of a transceiver relative to a transmitter. As previously set forth, this reduces the life of the battery quicker or requires a more expensive battery to further increase the cost.
The present invention solves the foregoing problems by using a data transmission device to randomize the transmissions of data packets through creating a variable transmission time interval for each data transmission. This randomization is created solely at the transmitter.
The data transmission device of the present invention also reduces the transmission time interval for each data packet in comparison with presently available data transmission devices. This decreases the time that a battery is turned on to reduce the power used. This allows use of a low cost battery while extending the life of the low cost battery.
To utilize a low power and low cost battery for relatively long periods of time such as two to five years, for example, the circuitry of the data transmission device of the present invention must be inactivated most of the time. Of course, there is current leakage even when the transmitter and its controlling microprocessor are turned off. Therefore, even when the microprocessor is turned off so as to be in a low power xe2x80x9csleepxe2x80x9d mode (inactivated), there is leakage, but it is very small so that this creates the low power xe2x80x9csleepxe2x80x9d mode.
When the data transmission device of the present invention is shipped, it is important that the transmitter remain in a state in which it cannot transmit. This avoids reducing the life of the battery when the data transmission device of the present invention is not in use to power the microprocessor and the transmitter for transmission of data.
The transmitter could be activated by electrical noise during shipment. The microprocessor has software to prevent this inadvertent activation of the transmitter.
The data transmission device of the present invention is sealed in an enclosure. Thus, the battery cannot be manually disconnected during shipping; this is how previously available data transmission devices have prevented the transmitter from being turned on.
Accordingly, a multiple function push button switch is interfaced to the microprocessor, which controls transmission of the data packet by the transmitter. The push button switch provides activation and inactivation of the transmitter. The push button switch also enables testing of clock hardware settings and correction of them, if necessary, when the push button is manually depressed for a predetermined time period (103 milliseconds).
The microprocessor has software to enable the transmitter to respond to different periods of time that the multiple function push button switch is held in its closed position. The multiple function push button switch has four functions.
One of the four functions is to turn on the microprocessor. A second function is to inactivate the microprocessor for the longest available period of time by the multiple function push button switch being held in its closed position for the longest period of time (4 seconds).
A third function is to indicate to any receiver, which receives the transmitter""s signals, that the microprocessor is being serviced by a human being through providing a service mark in the data packet transmitted when the multiple function push button switch is held in its closed position for at least 103 milliseconds but less than 4 seconds. This period of time insures that there is a transmission of a data packet.
A fourth function is to perform the initial reset after a battery is installed at the microprocessor. This fourth function avoids the need for conventional reset hardware since no reset is required by the circuitry of the data transmission device of the present invention. This is accomplished by configuring a clock, which is external of the microprocessor and provides a fixed periodic signal to awaken the microprocessor for a very short maximum period of time of 3 milliseconds, for example, every second.
The software in the microprocessor also insures that the transmitter will not be activated by electrical noise as could occur, for example, when the data transmission device of the present invention is being shipped since the microprocessor and the transmitter are powered on by pulse signals. Electrical noise can be interpreted as a pulse signal.
The data in the data packet is encoded in a form to reduce the transmission time of the data packet while increasing the transmission range of the transmitter. A shorter transmission time of each data packet decreases the possibility of collisions between data packets from two or more transmitters in the same environment.
An object of this invention is to provide a relatively low power wireless transmitter.
Another object of this invention is to provide random transmission of data packets by a wireless transmitter.
A further object of this invention is to provide a relatively low cost wireless transmitter.